1. Field of the Invention
The present invention relates to suspension systems for vehicle seats. More particularly, the invention relates to integrating an adjustable damping mechanism with the seat suspension system which provides for locking up any travel of the seat during vehicle conditions usually indicative of an accident.
2. Description of the Problem and Background Art
Suspension systems for vehicle seats ideally simultaneously isolate vehicle occupants from vibration due to road conditions, allow the driver to select seat height and seat position for comfort, visibility and sure access to the controls, and prevent excess sustained physical dislocation of the seat due to hard vehicle cornering or deceleration.
In commercial trucks, seat suspension systems frequently employ an adjustable air spring, which is provides isolation from road vibration and can readily be used to set seat height. U.S. Pat. No. 5,799,922 to Timms et al., discloses one such an air suspension device based on an air spring and having a cross or scissors linkage for positioning an occupant seat. U.S. Pat. No. 4,946,145 to Kurabe discloses an air suspension device for a seat with bidirectional control of the air supply to the air spring, determined by the occupant's selection of a preferred seat height and detection of the occupants weight.
However, a simple spring does not function well in maintaining a consistent seat height in a moving vehicle. The seat will tend to oscillate up and down under the influence of repeated shocks and vibration and will assume a different equilibrium height during periods when the apparent load changes due to acceleration or cornering. As in primary vehicle suspension systems, seat suspension systems benefit from the addition of elements which operate against seat movement and force the decay of unwanted seat movement.
Generally speaking, there are three types of suspension system, each of which deals with the oscillation and displacement issue somewhat differently. Passive suspension systems may be constructed from a spring and a fixed rate motion damping device such as a viscous fluid or friction shock absorber. Semi-active suspension systems may also be based on a spring and a shock absorber, but provide mechanisms for adjusting the damping rate of the shock absorber. Active suspension systems operate by, in effect, dynamically adjusting the direction and magnitude of the force applied to the seat in response to a number of factors relating to vehicle conditions and operation. Unlike passive and semi-active systems, active suspension systems can add energy to the system.
Because passive suspension systems are based on fixed rate springs and shock absorbers, they are in effect a tuned system, which is optimized for a frequency of vibration or displacement determined by the seat occupant's weight. Meeting the objectives of vibration isolation and maintaining consistent seat height depends on optimizing seat suspension performance for high frequency vibration isolation and low frequency seat displacing forces, respectively. Such goals are inherently inconsistent for a system tuned for a single frequency.
Semi-active seat suspension systems, at the cost of some added complexity, are directed to overcoming some of the frequency linked limitations of passive suspension systems. U.S. Pat. No. 5,652,704 to Catanzarite illustrates such a system in a patent directed to a method for the dynamic control of the damper. The seat suspension system of the patent provides an air spring and an electrorheological or magnetorheological motion damping element. A variety of sensors, including a seat occupant sensor and a roll over sensor are monitored by a microprocessor which adjusts the viscosity of the working fluid in the preferred magnetorheological motion damping device to change the operating characteristics of the suspension system.
While occupant comfort is an important objective, under extreme conditions of vehicle motion, particularly those that can occur during and after a collision, the restriction of occupant movement, particularly vertical driver movement can be a safety consideration. For example, extreme vertical movement of the driver can prevent the driver from reaching with his or her feet the brake, clutch and accelerator pedals. Driver movement may also change the driver's position relative to other the controls. Air spring based seat suspensions can contribute to the problem of driver movement by providing an energy reserve urging movement of the seat in the same direction as the driver. Floor mounted belts, if in use by the driver or occupant, partially restrict movement of the seat by squeezing the driver into the seat when the seat moves upward and forward relative to the vehicle during a collision. However, interaction between the belt and movement of the seat can contribute to the driver "submarining", that is, the driver being pulled partly below the dash.
The present inventor is aware of a product of the Indiana Mills and Manufacturing, Inc., of Westfield, Ind. which is directed to this issue. The product provides a collision sensing element which when activated triggers a cam element driven by pyrotechnic elements for greatly tightening the belt on the driver or occupant and using the driver to pull the seat downwardly. While effective, the driver would be treated less roughly if the seat itself were restrained instead of the driver. U.S. Pat. 5,344,204 provides a seat positioning mechanism operating independently of the seat suspension system which repositions the seat rearwardly in response to detection of accident conditions. The system of the '204 patent it adds to the complexity and expense the seat installation.